#define _USE_MATH_DEFINES
#include <string>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <fstream>
#include <deque>
#include <vector>
#include <utility>

using namespace std;

int main()
{

    ifstream in("input.txt");
    ofstream out("output.txt");

    char masa[100][100];
    char masb[100][100];

    int n, m,count = 0;
    in >> n >> m;
    string s1,s2;

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            in >> masa[i][j];
        }
    }

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            in >> masb[i][j];
        }
    }



    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            if (masa[i][j] != '.') {
                if (masa[i][j] != masb[i][j]) {
                    count++;
                    if (islower(masa[i][j])) {
                        s2.push_back(masa[i][j]);
                    }
                    else {
                        s1.push_back(masa[i][j]);
                    }
                }
            }
        }
    }


    out << count << endl;
    sort(s1.begin(), s1.end());
    sort(s2.begin(), s2.end());
    out << s2 << s1;

    out.close();
    in.close();
    return 0;
}